Objective  As one of the basic physical fields of the earth, gravity field reflects the distribution of underground materials and the changes of space and time. It has important value in resource exploration, military application and space science research. At present, the measurement methods of earth gravity field include aerial gravimetry, marine gravimetry, satellite gravimetry and ground gravimetry, et al. As an important method of gravity field measurement, ground gravimetry is mainly used for local fine construction of earth gravity field, which can be divided into ground static gravimetry and ground dynamic gravimetry. Due to the high cost and low efficiency of ground static gravimetry, ground dynamic gravimetry is usually adopted, namely ground vehicle gravimetry. At present, strapdown inertial navigation system (SINS)/global navigation satellite system (GNSS) integrated system is usually used in vehicle gravimetry, which lacks autonomy and has limited accuracy in the special environment where GNSS signal is blocked. To solve this problem, this paper proposes a strapdown vehicle autonomous gravimetry method based on two-dimensional laser Doppler velocimeter (LDV).

  Methods  In this paper, a high-precision autonomous vehicle gravimetry method is designed. In order to improve the autonomy of the system, SINS/LDV integrated system is adopted in this paper, which does not need to rely on external signal sources. In order to ensure the measurement accuracy of the system, the LDV adopted by the system is two-dimensional, which is sensitive to the velocity of the vertical direction, so as to reduce the measurement error. The systematic errors are analyzed, and the constraints on the device accuracy and measurement scheme of LDV are proposed (Tab.1). The data processing flow of SINS/LDV integrated gravimetry system is also proposed. The system can finally realize the high-precision gravimetry in special environment.

  Result and Discussions  The experiment was conducted in a special environment. During the experiment, the altitude changed greatly (Fig.4) and the GPS was seriously blocked (Fig.5). There are altogether 6 repeated lines in the experiment, each of which is about 11 km. During the experiment, the maximum horizontal error of SINS/LDV integrated navigation is about 17 m (Fig.8), and the maximum height error is about 2 m (Fig.9), which meets the requirements of system standard (Tab.1). Gravity anomaly were calculated according to the results of integrated navigation. The six lines based on SINS/LDV integrated system had a good consistency, and the maximum and minimum internal coincidence accuracy of a single survey line are 1.05 mGal and 0.47 mGal, and the total internal coincidence accuracy is 0.70 mGal (Tab.2). However, the consistency of the six lines based on SINS/GNSS integrated system are relatively poor. The maximum and minimum accuracy of internal coincidence of a single line are 2.46 mGal and 1.02 mGal, and the total internal coincidence accuracy is 1.53 mGal (Tab.3). The accuracy of SINS/LDV integrated system is generally better than that of SINS/LDV integrated system, and the total accuracy of SINS/LDV integrated system is about 54% higher than that of SINS/GNSS integrated system.

  Conclusions  In this paper, a strapdown vehicle autonomous gravimetry method based on two-dimensional laser Doppler velocimeter is studied. The measurement principle and error model of the system are analyzed, and the corresponding index and data processing flow of the system are given. The vehicle gravimetry experiment shows that the consistency of the six lines in SINS/LDV integrated gravimetry system is high, while that of the six lines in SINS/GNSS integrated gravimetry system is relatively poor when the satellite signal is seriously blocked. Accordingly, the single internal coincidence accuracy of SINS/LDV integrated system is generally better than that of SINS/GNSS integrated system, and the total internal coincidence accuracy of SINS/LDV integrated system is nearly half higher than that of SINS/GNSS integrated system. The experimental results show that SINS/LDV integrated gravimetry system can realize gravimetry, and the gravimetry accuracy is higher than SINS/GNSS integrated gravimetry system in special measuring environment. The research of this paper provides technical support for the vehicle gravimetry in the environment when the GNSS signal is blocked, and the relevant results can be applied in geological exploration, gravity matching and the refinement of the earth's local gravity field.